The present invention relates to a method and apparatus for the replacement of contaminated high efficiency particulate air (HEPA) filters, and more particularly relates to a method and apparatus for the replacement of contaminated HEPA filters without contamination of the surrounding environment.
High efficiency particulate air (HEPA) filters are widely used in the nuclear, pharmaceutical, medical, and microelectronics industries for the removal of microscopic contaminants from exhaust gases. For example, HEPA filters may be found in any glovebox containing radioactive or other hazardous materials. HEPA filters were first used by the nuclear industry over 40 years ago and were typically placed in a square wooden container fitted into the exhaust ducting. Current installations have not changed much from this early design. Such filters must be replaced periodically to maintain filtering efficiency.
A problem with the conventional type of installation is that, for nuclear and other hazardous applications, when it becomes necessary to change out the filter, generally every year or two, it is a difficult, time consuming, and expensive process. Typically the change-out of a contaminated filter involves opening the filter housing, removing the dirty filter into a change-out bag, replacing the contaminated filter with a clean filter and resealing the housing. The area where the change-out takes place may be sealed during the change-out, or the surrounding area must be decontaminated after change-out, before normal activities can be resumed. Several attempts have been made to develop systems for the clean bag-out of contaminated filters, but so far, none have found wide-spread acceptance in the industry.
A need exists for a method and apparatus for the replacement of contaminated HEPA filters without contamination of the surrounding environment.
It is an object of the invention to provide an improved method and apparatus for the replacement of contaminated HEPA filters.
It is another object of the invention to provide an improved method and apparatus for the replacement of contaminated HEPA filters without contamination of the surrounding environment.
It is another object of the invention to provide an improved method and apparatus for the replacement of contaminated HEPA filters substantially without negative effect and that overcome many of the disadvantages of prior arrangements.
In brief, a method and apparatus are provided for the replacement of contaminated HEPA filters without contamination of the surrounding environment. A filter housing is generally cylindrical and defines a filter receiving cavity. The filter housing has a filter receiving end and a filter removing end. An active HEPA filter is received within the filter housing cavity and is moved to a location near the filter removing end. A backup HEPA filter is received within the filter housing cavity and is located near the filter receiving end. A change-out bag is sealed to the filter housing and is stored in the filter housing cavity adjacent to the filter removing end. The filter housing allows a gas to flow through the active HEPA filter without passing through the backup HEPA filter. After a period of operation, the active filter becomes contaminated.
For the replacement of a contaminated HEPA filter, flow valves are closed, then end covers are removed from the filter receiving end and the filter removing end of the filter housing and the change-out bag is opened. A new HEPA filter is used to push the backup HEPA filter into the position of the active HEPA filter, thereby pushing the contaminated HEPA filter into the change-out bag during filter replacement. The change-out bag is then sealed to isolate the contaminated HEPA filter for disposal. The old backup HEPA filter is now the active filter, and the new HEPA filter becomes the backup.